Earlier work has shown that embryos of three avian species, chickens, pheasants and Japanese quail, respond to injection of organophosphorous pesticides by developing a syndrome of abnormalities combining micromelia and parrot beak, while those of a fourth species, Bobwhite quail, respond with a different syndrome combining crooked neck and amuscular development. Current studies focus on one of this group of compounds, Azodrin, which appears to be a prototype teratogen, being effective at very low levels, easily solubilized, and with teratogenic levels well separated from lethal levels, permitting study of the sequence of changes in cells, tissues and organs in treated embryos from first onset of symptoms through the entire developmental period. In addition to the species difference, chickens have shown some evidence of variation in sensitivity to this pesticide and the compound has been shown to interact with nicotinamide. Sine analogues of nicotinamide also produce the two syndromes noted above when injected into embryonated chicken eggs, and since mutants of both syndromes are available, the work to be undertaken during this year will be directed toward further investigations of genetic variation in response and an effort to develop further evidence on the basis of the teratogenic action of Azodrin. Minimal effective levels and sensitive periods in embryos of several genotypes will be established, and histological and fine structural studies of the integument and the gut in embryos receiving several levels of treatment will be completed.